Relief plates from polymer with terminal unsaturation

ABSTRACT

It has been found that excellent quality photopolymer printing plates having hardness, flexibility, resilience, abrasion resistance and resistance to alcohol-based inks can be prepared from photopolymer compositions comprising a liquid polymer containing at least two terminal olefin groups attached to the polymer through a combination of at least two ether, thioether, ester, keto or amide groups, from about 1 to about 50% by weight based on the polymer of at least one ethylenically unsaturated monomer, from about 0.1 to about 10% by weight of a photoinitiator and about 0.01 to about 2% of a stabilizer.

This is a division of application Ser. No. 810,334, filed June 27, 1977,now U.S. Pat. No. 4,137,081, which is in turn a continuation-in-part ofapplication Ser. No. 628,862, filed Nov. 5, 1975, now abandoned.

This invention relates to photopolymer compositions, processes formaking printing reliefs and to photopolymer elements. More particularly,this invention relates to liquid, water dispersible photopolymercompositions which on exposure to actinic radiation will givecross-linked structures having hardness, flexibility, resilience,abrasion resistance and resistance to alcohol-based inks; photopolymerplates embodying a layer of such composition; and the process of makingprinting plate reliefs from such compositions.

Compositions capable of being converted under the influence of actiniclight to solid, insoluble, tough structures are well-known and havebecome increasingly important in the preparation of printing plates. Oneof the fundamental patents relating to such compositions in U.S. Pat.No. 2,760,863 to Plambeck. In the process of the Plambeck patent,printing plates are produced directly by exposing to actinic lightthrough an image-bearing process transparency a layer of an essentiallytransparent composition containing an addition polymerizable,ethylenically unsaturated monomer and an addition polymerizationinitiator activatable by actinic light. The layer of polymerizablecomposition is supported on a suitable support, and exposure of thecomposition is continued until substantial polymerization of thecomposition has occurred in the exposed areas with substantially nopolymerization occurring in the nonexposed areas. The unchanged materialin the latter areas then is removed, as by treatment with a suitablesolvent in which the polymerized composition in the exposed areas isinsoluble. This results in a raised relief image which corresponds tothe transparent image of the transparency and which is suitable for useas a printing plate, as in letterpress and dry off-set work.

Photopolymerizable layers of the type of the Plambeck patent generallyare prepared from polymeric components which are soluble in organicsolvents. Accordingly, development of printing plates based on suchcompositions has required the use of organic solvents or of solutionscontaining high percentages of organic solvents. Due to the toxicity,high volatility and generally low flash point of low cost organicsolvents, their use often gave rise to hazardous conditions. As aconsequence, further research was directed and led to the development ofseveral photopolymer layers which are soluble in water or aqueousalkali. For example, these layers have utilized polymeric componentscontaining lateral acid groups, or the soluble salts thereof or certainwater-soluble polymer compositions. In U.S. Pat. No. 3,794,494 water oraqueous alkali dispersible compositions are described suitable for usein rigid or elastic flexographic printing plate preparation. Thesecompositions comprise combinations of unsaturated polyesters,polyunsaturated monomers and a photopolymerization initiator. However,flexible printing plates suitable for use in flexographic printing usingalcohol-based inks cannot be prepared using compositions of the typedescribed in the patent because the quick drying alcohol-based inks usedin flexographic printing will cause the cured compositions to swell anddisintegrate.

It has now been discovered that excellent quality photopolymer printingplates having hardness, flexibility, resilience, abrasion resistance andresistance to alcohol-based inks can be prepared from certain uniquephotopolymer compositions in accordance with this invention. Thephotopolymer composition of this invention comprises (1) a liquidpolymer containing at least two terminal olefin groups attached to thepolymer through a combination of at least two ether, thioether, ester,keto, or amide groups, (2) from about 1 to about 50% by weight based onthe liquid polymer of at least one ethylenically unsaturated monomerselected from the group consisting of acrylonitrile, styrene, methylsubstituted styrenes, N-vinyl pyrrolidone, and a monomer having itsunsaturation in the form of at least one ##STR1## wherein R is hydrogenor a C₁ -C₃ alkyl group, (3) from about 0.1 to about 10% by weight of aphotoinitiator, and (4) about 0.01 to about 2% of a thermalpolymerization inhibitor.

While the photopolymer compositions of this invention are notwater-soluble, they are sufficiently water-dispersible so that unexposedportions of printing plates prepared from said compositions can beremoved by washing with dilute aqueous solution of a detergent.Particularly useful detergents are anionic detergents such as olefinsulfonates.

The photopolymer compositions of this invention can readily be appliedto a support, such as for example polyester film or a grained-metalsheet, from solution or by conventional coating procedures. Such layerswill generally be from 3 to 250 mils in thickness. After exposurethrough a process transparency, the compositions are readily developablewith an aqueous detergent solution to form printing reliefs, thusobviating the need for organic solvents, although organic solvents maybe used either alone or in combination with water, if desired.

EXAMPLE 1

This example illustrates the use of a liquid polymer prepared fromcarboxyl terminated polybutadiene and glycidyl methacrylate, in aphotopolymer composition in accordance with this invention.

Into a round bottom flask fitted with a stirrer, a reflux condenser, andan air sparge tube, is charged 3272 parts of a carboxyl terminatedpolybutadiene (sold by B. F. Goodrich Co. under the trademark "HycarCTB"-2000X162) and 2.61 parts sodium methoxide catalyst. The mixture isheated with stirring while a stream of dry air is passed through. Whenthe temperature reaches 100° C., 229 parts of glycidyl methacrylate areadded, along with a mixture of thermal stabilizers comprising 0.26 partnitrobenzene, 0.49 part phenothiazine and 6.55 parts ofdi-tert-butyl-para-cresol. The reaction mixture is maintained at atemperature of 100° C. for 11 hours. The resulting terminallyunsaturated polymer has an acid number of 2.8 and a Brookfield viscositymeasured at 25° C. of 92,410 cps.

A portion of the above prepared polymer, comprising 3087 parts, isstirred together with a mixture of unsaturated monomers comprising 210.5parts of 1,6-hexanediol dimethacrylate and 210.5 parts of laurylmethacrylate and 140.3 parts of 2,2-diethoxyacetophenone photoinitiator.This mixture is stirred at room temperature for one hour, at which timeit is completely homogeneous. The resulting photopolymer composition hasa Brookfield viscosity measured at 25° C. of 21,200 cps.

The above prepared photopolymer composition is then poured into a rubberframe 2 mm. thick. A glass plate is placed over the frame in contactwith the composition. The composition is then exposed through the glassplate at room temperature for 60 seconds to a bank of 10 30-wattultraviolet fluorescent lights (Westinghouse F30T8/BL) set at a distanceof 7 cm. from the glass. The glass plate with the photopolymercomposition attached is separated from the mold and immersed in a washbath containing an aqueous solution of 1.0% α-olefin sulfonate detergent(sold by Stepan Chemical Corporation under the trademark "Bioterg"). Theuncrosslinked liquid composition is dispersed in the aqueous solution.The portion of composition next to the glass (nearest the ultravioletlights) is hardened. The thus hardened composition is peeled from theglass and dried. It is found to have a thickness of 0.014 inch.

EXAMPLE 2

This example illustrates the physical properties of the cross-linkedphotopolymer composition described in Example 1.

A sample of the photopolymer composition described in Example 1 isspread to a thickness of 0.04 inch on a glass plate using a doctorblade. The composition is covered with a 0.004 inch polyester film andexposed to ultraviolet lights as described in Example 1 for 20 secondsthrough the polyester film. The composition is then exposed through theglass plate to a 3 kilowatt medium pressure mercury arc lamp for 4.5minutes. The polyester film is peeled off the cross-linked compositionand the hardened composition in turn peeled off the glass. Dumbbellshaped samples are cut from the cross-linked composition and used todetermine its physical properties. The cross-linked composition has atensile strength of 240 psi, an elongation of 70%, a tensile modulus of470 psi, a Bayshore resilience of 47%, and a Shore A hardness of 52.

EXAMPLE 3

This example illustrates the solvent resistant properties of thecross-linked photopolymer composition described in Example 1 in varioussolvents.

Samples of cross-linked photopolymer composition are prepared in athickness of 50 mils as described in Example 2 and tested in varioussolvents. The percent weight gain and change in Shore A hardness aretabulated in Table I below:

                  TABLE I                                                         ______________________________________                                        SOLVENT RESISTANCE OF CROSS-LINKED                                            PHOTOPOLYMER COMPOSITION                                                                          %                                                                             Weight Gain                                                                              Change in Shore A                              Run  Solvent        (x)        Hardness                                       ______________________________________                                        a    Water          0          +2                                             b    Methanol       2          0                                              c    Ethanol        2          0                                              d    N-propanol     4          -2                                             e    Isopropanol    3          -2                                             f    Ethylene glycol                                                                              -1         +1                                             g    Propylene glycol                                                                             -1         +1                                             h    Diethylene glycol                                                                            -1         0                                              i    Cellosolve     10         -7                                             j    Butyl cellosolve                                                                             13         -1.4                                           k    Acetone        20         -3                                             l    Methyl Ethyl Ketone                                                                          50         -4                                             m    Ethyl acetate  62         -4                                             n    Heptane        75                                                        disintegrated                                                                 o    Kerosene       82         -4                                             p    Xylene         --                                                        disintegrated                                                                 q    Perchloroethylene                                                                            --                                                        disintegrated                                                                 r    90% Denatured ethyl                                                                          5          -2                                                  alcohol                                                                       10% Ethyl acetate                                                        s    80% Denatured ethyl                                                                          9          -5                                                  alcohol                                                                       20% Ethyl acetate                                                        t    77% Water      1.5        1.5                                                 17% Isopropanol                                                                6% NH.sub.4 OH-Conc.                                                    ______________________________________                                         (x)After 24 hours immersion in solvent at room temperature, samples 50        mils thick, polyester substrate sheet attached.                          

EXAMPLE 4

This example illustrates the use of a liquid polymer prepared fromcarboxyl terminated butadiene-acrylonitrile copolymer and glycidylmethacrylate, in a photopolymer composition in accordance with thisinvention.

Into a flask equipped as described in Example 1 is charged 536 parts ofa carboxyl terminated butadiene-acrylonitrile copolymer, having an acidnumber of 31.1 and containing 17% acrylonitrile, 98.0 parts of glycidylmethacrylate, 0.43 parts of sodium methoxide catalyst and 2.41 parts ofdi-tert-butyl-para-cresol stabilizer. The reaction mixture is stirredand heated at a temperature of 100° C. for 5 hours. The resultingterminally unsaturated polymer has an acid number of 0.8.

A portion of the above prepared polymer, comprising 440 parts is stirredtogether with a mixture of unsaturated monomers comprising 30 parts of1,6-hexanediol dimethacrylate and 30 parts of lauryl methacrylate and 20parts of 2,2-diethoxyacetophenone photoinitiator until it is completelyhomogeneous. A sample of the resulting photopolymer composition isstored in the dark for 50 days at a temperature of 60° C. After storagethe composition is examined and found not to have gelled.

A sample of the above prepared photopolymer composition is poured into arubber frame and a glass plate placed over the frame in contact with thecomposition. The composition is then exposed through the glass plate toultraviolet light exactly as described in Example 1. A 0.017 inch layerof cross-linked (i.e. hardened) composition is formed next to the glassplate.

Specimens of the cross-linked photopolymer composition 50 mils thick areprepared and tested to determine physical properties exactly asdescribed in Example 2. The cross-linked composition is found to have atensile strength of 360 psi, an elongation of 70%, a tensile modulus of736 psi, a Bayshore resilience of 37% and a Shore A hardness of 59.Specimens soaked in ethyl alcohol for 24 hours at room temperature gain6% in weight. Specimens soaked in isopropanol under the same conditionsgain 8% in weight.

EXAMPLE 5

This example illustrates the use of a liquid polymer prepared from amineterminated butadiene-acrylonitrile copolymer and glycidyl methacrylate,in a photopolymer composition in accordance with this invention.

Into a flask equipped as described in Example 1 is charged 934.8 partsof an amine terminated butadiene-acrylonitrile copolymer (sold by B. F.Goodrich Co. under the trademark "Hycar ATBN"), 374 parts of glycidylmethacrylate and a mixture of thermal stabilizers comprising 0.07 partof nitrobenzene, 0.14 part of phenothiazine and 1.87 parts ofdi-tert-butyl-para-cresol. The reaction mixture is stirred and heated ata temperature of 60° C. for 4 hours.

A portion of the resulting terminally unsaturated polymer, comprising246 parts is stirred together with a mixture of unsaturated monomerscomprising 18 parts of 1,6-hexanediol dimethacrylate and 18 parts oflauryl methacrylate, 12 parts of 2,2-diethoxyacetophenone photoinitiatorand 1.2 parts of di-tert-butyl-para-cresol stabilizer, for one hour atroom temperature.

A 40 mil layer of the resulting photopolymer composition is cross-linkedby exposure to a 3 kilowatt medium pressure mercury arc lamp for 3.5minutes. Samples of the cross-linked composition are tested for physicalproperties and found to have a tensile strength of 2100 psi, anelongation of 32%, a tensile modulus of 23,200 psi, and a Shore Ahardness of 88.

EXAMPLE 6

This example illustrates the use of the photopolymer compositiondescribed in Example 1 in the preparation of a printing plate.

A portion of the photopolymer composition described in Example 1 isspread in a 0.067 inch thick layer on a 4 mil polyester backing sheet(support) and exposed through an image bearing negative transparency toa 3 kilowatt medium pressure mercury arc lamp for 6 minutes. Theuncrosslinked photopolymer composition is washed away using an aqueoussolution of 1.0% α-olefin sulfonate (Bioterg®) at 50° C. The resultingprinting plate is dried, and post-cured by exposing under a nitrogenatmosphere to a bank of 10 30-watt ultraviolet fluorescent lights for 12minutes. The resulting printing plate is completely tack-free.

The thus prepared printing plate is mounted on a flexographic printingpress and the press run at a speed of 250-300 fpm. until approximately10,000 impressions are made. The ink used during the press run is a redflexographic ink containing as solvents 3% methyl alcohol, 73% ethylalcohol, 10% isopropyl alcohol, 10% ethyl cellosolve and 4% water. Oncompletion of the press run the plate is visually examined and shows nosign of wear, swelling or tack. The printed impressions are of highquality.

EXAMPLE 7

This example illustrates the use of the terminally unsaturated polymerdescribed in Example 1 in various photopolymer compositions.

In each case the terminally unsaturated polymer containing the mixtureof thermal stabilizers as described in Example 1 is stirrer with one ormore unsaturated monomers and a photoinitiator to form a photopolymercomposition. Samples for the testing of physical properties are spreadto a thickness of 50 mils on a glass plate and covered with an 0.004inch polyester film. Each sample is then exposed to ultraviolet lightthrough the polyester film as described in Example 1 for one minute andthen through the glass plate to a 3 kilowatt medium pressure mercury arclamp for 4 minutes. Additional samples are prepared the same way exceptthey are only exposed to the ultraviolet light through the polyesterfilm for periods of time ranging from 30 to 180 seconds. The componentsof the photopolymer compositions, the thickness of the cross-linkedlayers formed on exposure for 30 to 180 seconds and the physicalproperties of the samples completely cross-linked are recited below inTable II.

                                      TABLE II                                    __________________________________________________________________________    Components of Photpolymer                                                     Composition            Parts per Hundred                                      Terminally unsaturated polymer                                                                       88  88  88  88  88  88  88  88  88  77                 Lauryl Methacrylate    6   4.2 7.8 6   6   6   6   6   12  --                 1,6-Hexanediol dimethacrylate                                                                        6   7.8 4.2 6   6   --  --  --  --  23                 Tetraethylene glycol dimethacrylate                                                                  --  --  --  --  --  6   --  --  --  --                 Polypropylene glycol dimethacrylate                                                                  --  --  --  --  --  13  6   --  --  --                 1,3-Butylene glycol dimethacrylate                                                                   --  --  --  --  --  --  --  6   --  --                 2,2-Diethoxyacetophenone (photoinitiator)                                                            4   4   4   6   --  4   4   4   4   --                 Benzoin isobutyl ether (photoinitiator)                                                              --  --  --  --  1.0 --  --  --  --  1.8                                       Thickness in mm                                        Thickness in mm of cross-linked layer after                                   exposure for the following period of time:                                     30 sec.               --  --  --  --  0.10                                                                              0.12                                                                              --  --  --  0.35                60 sec.               0.21                                                                              0.25                                                                              0.23                                                                              0.26                                                                              0.29                                                                              0.36                                                                              0.32                                                                              0.24                                                                              0.19                                                                              0.68                90 sec.               0.39                                                                              0.40                                                                              0.41                                                                              0.41                                                                              0.52                                                                              0.48                                                                              0.48                                                                              0.37                                                                              0.31                                                                              0.83               120 sec.               0.50                                                                              0.51                                                                              0.52                                                                              0.55                                                                              0.63                                                                              0.58                                                                              0.60                                                                              0.50                                                                              0.39                                                                              1.12               180 sec.               0.69                                                                              0.70                                                                              0.71                                                                              0.75                                                                              0.89                                                                              0.74                                                                              0.76                                                                              0.68                                                                              0.56                                                                              1.25                                      Physical Properties                                    Tensile Strength - psi.sup.a                                                                         220 230 200 230 220 180 170 270 150 --                 Elongation - %         70  60  80  70  80  80  80  80  100 --                 Tensile Modulus - psi  400 470 331 370 373 206 290 430 360 --                 Shore A Hardness       47  52  42  42  46  42  40  48  44  83                 Resilience - %.sup.b   46  47  44  44  44  44  44  44  50  --                 % Weight gain in ETOH.sup.c                                                                          2   2   2   2   2   4   4   2   2   3                  __________________________________________________________________________     .sup.a Tensile properties are measured with an Instron tester using 2         inches/min. crosshead speed.                                                  .sup.b Resilience measured on a stack of 5 samples, each 50 mils thick, %     return after steel ball dropped from 30 cm.                                   .sup.c Samples soaked in ethyl alcohol for 24 hours at a temperature of       25° C.                                                            

EXAMPLE 8

This example illustrates the use of a vinyl terminatedbutadiene-acrylonitrile copolymer in a photopolymer composition inaccordance with this invention.

A portion, comprising 77 parts, of a vinyl terminatedbutadiene-acrylonitrile copolymer (sold by B. F. Goodrich Co. under thetrademark "Hycar VTBN" - 1300X14, containing 17% acrylonitrile andhaving a number average molecular weight of approximately 3400) isstirred together with 23 parts of tetraethylene glycol dimethacrylate(unsaturated monomer), 1.8 parts of benzoin isobutyl ether(photoinitiator) and 0.1 part of di-tert-butyl-para-cresol (stabilizer)until the composition is completely homogeneous (about one hour).

The above prepared photopolymer composition is poured into a rubberframe, covered with a glass plate and exposed to a bank of ultravioletlights as described in Example 1. A layer 0.043 inch thick ofcross-linked composition is formed. A sample of the cross-linkedcomposition swelled 7% after soaking for 24 hours at room temperature inethyl alcohol.

EXAMPLE 9

This example illustrates the use of a mixture of ethylenicallyunsaturated monomers containing N-vinyl-2-pyrrolidone in accordance withthis invention.

A portion, comprising 520 parts of the terminally unsaturated polymer,prepared by reacting carboxyl terminated polybutadiene with glycidylmethacrylate as described in Example 1, is blended with a mixture ofethylenically unsaturated monomers comprising 144 parts of laurylmethacrylate, 60 parts of 1,3-butylene glycol dimethacrylate and 76parts of N-vinyl-2-pyrrolidone and 4.8 parts of2,2-dimethoxy-2-phenylacetophenone photoinitiator at room temperatureuntil the mixture is completely homogeneous. The resulting photopolymercomposition has a Brookfield viscosity measured at 25° C. of 4100 cps.

A sample of the photopolymer composition is spread to a thickness of0.04 inch on a glass plate using a doctor blade, covered with apolyester film, exposed from both sides and tested to determine itsphysical properties, all as described in Example 2. The hardened resinhas a tensile strength of 780 psi, an elongation of 83%, a tensilemodulus of 813 psi, and a Shore A hardness of 64.

EXAMPLE 10

This example illustrates the use of an inert particulate filler in aphotopolymer composition in accordance with this invention.

A portion, comprising 180 parts of the terminally unsaturated polymerdescribed in Example 1, is blended with a mixture of ethylenicallyunsaturated monomers comprising 69 parts of lauryl methacrylate, 15parts of 1,3-butylene glycol dimethacrylate and 36 parts ofN-vinyl-2-pyrrolidone, 1.8 parts of 2,2-dimethoxy-2-phenylacetophenonephotoinitiator and 13.1 parts of fumed silica particulate filler at roomtemperature until the mixture is completely homogeneous. The resultingphotopolymer composition has a Brookfield viscosity measured at 25° C.of 6130 cps.

A 0.04 inch thick sample of the photopolymer composition is cured andtested to determine its physical properties, all as described in Example2. The cured resin has a tensile strength of 630 psi, an elongation of90%, a tensile modulus of 595 psi, and a Shore A hardness of 60.

As stated above, the terminally unsaturated polymers used in thephotopolymer compositions of this invention are liquid polymerscontaining at least two terminal olefin groups attached to the polymerthrough a combination of at least two ether, thioether, ester, keto oramide groups. These terminal olefinically unsaturated polymers will haveone of the following structures ##STR2## where X is selected from --O--,--S--, ##STR3## Y is selected from --O--CH₂ --CH═CH₂ and ##STR4## R' isselected from --H and --CH₃ groups; Z is selected from ##STR5## where R"is selected from --H, --CH₃ and ##STR6## and P is a polymer residueselected from liquid homopolymers of butadiene, isoprene, chloroprene,styrene, isobutylene, ethylene and copolymers of butadiene withacrylonitrile, butadiene with styrene, butadiene with isoprene, ethylenewith neohexene, isobutylene with styrene, and isobutylene withacrylonitrile and the corresponding saturated polymer residues.Preferably the above liquid polymers will have a molecular weight in therange of 1000 to 20,000, most preferably in the range of 3000 to 6000.It will be understood by those skilled in the art that if the polymerresidue above was prepared by free radical polymerization, it may retainconnecting groups originating from the free radical initiator employedin its preparation.

A typical liquid polymer employed in the photopolymer composition ofthis invention is one prepared by reacting a butadiene, isoprene,chloroprene, styrene, isobutylene, or ethylene polymer or abutadiene-acrylonitrile, butadiene-isoprene, butadiene-styrene, orethylene-neohexene copolymer containing carboxyl, amine, hydroxyl,thiol, oxirane, or aziridine terminal groups, or corresponding productsfrom which the olefinic unsaturation has been removed as byhydrogenation, with a glycidyl allyl ether, acrylate and copolymers ofthe type useful for preparing these terminally unsaturated polymers areprepared by a free radical polymerization using special catalysts or byanionic polymerization followed by capping the living polymer by carbondioxide, ethylene oxide, etc. as described in an article by French inRubber Chemistry and Technology, Vol. 42, pages 71-107 (1969). The stepof adding the terminal unsaturated group to the functionally terminatedpolymer (i.e. the second step in preparing the terminally unsaturatedpolymer) is not a polymerization.

More particularly, the polymers of structure I can be prepared byreaction of functionally terminated or telechelic polymers of the typedescribed by French in the Rubber Chemistry and Technology articlereferred to above, in which the terminal functional groups are carboxyl,hydroxyl, thiol or amine groups, with compounds such as allyl glycidylether, glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate,ethyl itaconate monoglycidyl ester or methyl fumarate monoglycidylester.

Polymers of structure II can be prepared by reaction of telechelicpolymers containing hydroxyl functional groups with acrylic ormethacrylic acid or the corresponding anhydride.

Polymers of structures III and IV can be prepared by reaction oftelechelic polymers containing oxirane and aziridine functional groups,respectively, with unsaturated polymerizable acids such as acrylic,methacrylic, or the monoalkyl esters of crotonic, itaconic, or fumaricacid.

Polymers of the structure V are vinyl ketone terminated telechelicpolymers.

In general the terminal olefinically unsaturated polymers employed inthe photopolymer composition of this invention are viscous liquids,having Brookfield viscosities, measured at 25° C., of between 1,000 and1,000,000 centipoises, most preferably between 20,000 and 100,000centipoises.

As an illustration of the type of reaction involved to introduce theterminal unsaturation into the low molecular weight polymers andcopolymers to prepare the polymers useful for this invention, thereaction between a carboxyl terminated polybutadiene and glycidylacrylate ##STR7## is represented below. ##STR8## As indicated two molesof epoxy compound react with each mole of olefin addition polymer.Generally, however, a slight excess of epoxide is used.

It is also possible to use a large excess of epoxy compound. In thiscase, chain extension occurs. The excess epoxide reacts with thehydroxyl groups formed by the initial reaction between the functionallyterminated olefin addition polymer and the epoxy compound. For example:##STR9##

These reactions can be run between 25° and 200° C. with a temperaturerange of 100°-125° being preferred. An acid or basic catalyst can beused to reduce the required reaction temperature and time. Some usefulcatalysts are sodium hydroxide, sodium ethoxide, triethylamine,triethylbenzyl ammonium chloride, hydrogen chloride, and borontrifluoride etherate. Generally, 0.001 to 5.0% by weight catalyst isused.

To make the polymer with only single terminal double bonds, close to astoichiometric amount of epoxide and a basic catalyst should be used. Tomake a chain extended polymer, a large excess of epoxide and an acidiccatalyst is preferred.

The ethylenically unsaturated monomer components of the compositions ofthis invention are selected from acrylonitrile, methacrylonitrile,styrene, methyl substituted styrenes, N-vinyl pyrrolidone, and compoundscontaining one or more ##STR10## wherein R is hydrogen or a C₁ -C₃ alkylgroup.

Useful monofunctional ethylenically unsaturated monomers includeacrylonitrile, methacrylonitrile, styrene, 2-methylstyrene, α,p-dimethylstyrene, N-vinyl pyrrolidone, acrylic acid, methacrylic acid,esters of acrylic acid and methacrylic acid containing up to 22 carbonatoms, acrylamide, mono- and di-N-alkyl substituted acrylamides andmethacrylamides containing up to 10 carbons in the alkyl group, anddiacetone acrylamide.

A useful trifunctional monomer is1,3,5-triacryloylhexahydro-1,3,5-triazine. This compound and relatedcompounds such as the corresponding methacryloyl derivative have thestructural formula ##STR11## wherein R is hydrogen or a C₁ -C₃ alkylgroup.

Other suitable difunctional monomers may be defined by the structuralformula ##STR12## wherein R again is hydrogen or a C₁ -C₃ alkyl group;both X's are either --NH-- or --O-- and A is alkylene, substitutedalkylene or alkylene oxy alkylene, A preferred monomer having thisformula is N,N'-oxydimethylene-bis(acrylamide).

When X' in formula II above is --NH--, but A is alkylene or substitutedalkylene, this is descriptive of another preferred monomer,N,N'-methylene-bis(acrylamide). This compound is one member of avaluable group of monomers represented by compounds having the formula##STR13## wherein R is hydrogen or a C₁ -C₃ alkyl group, R₁ is hydrogen,a C₁ -C₃ alkyl group or phenyl, n is 1 to 6 and the total number ofcarbon atoms in --(CHR₁)_(n) -- is no more than 10.

Representative of compounds of formula III above areN,N'-methylene-bis(acrylamide), N,N'-methylene-bis(methacrylamide),N,N'-methylene-bis(2-ethylacrylamide),N,N'-methylene-bis(2-propylacrylamide), N,N'-ethylene-bis(acrylamide),N,N'-ethylene-bis(methacrylamide),N,N'-(1,6-hexamethylene)-bis(acrylamide),N,N'-(1,6-hexamethylene)-bis(methacrylamide),N,N'-ethylidene-bis(acrylamide), N,N'-ethylidene-bis(methacrylamide),N,N'-benzylidene-bis(acrylamide), N,N'-butylidene-bis(methacrylamide)and N,N'-propylidene-bis(acrylamide). These compounds may be prepared byconventional reaction well known in the art, as for example, in U.S.Pat. No. 2,475,846.

Also useful monomers are those wherein X' in formula II above is --O--.When A is alkylene or substituted alkylene, the compounds are di-,tri-and tetra-acrylates of certain polyhydric alcohols. These acrylatesmay be illustrated by the general formula ##STR14## wherein R ishydrogen or a C₁ -C₃ alkyl group, a is 0 or 1, R₂ is hydrogen, a C₁ -C₃alkyl group, ##STR15## R₃ is hydrogen, a C₁ -C₃ alkyl group, --CH₂ OH or##STR16## n is 1 to 6 and the total number of carbon atoms in --(CR₂R₃)_(n) -- is no more than 11. Representative of these compounds areethylene glycol diacrylate, ethylene glycol dimethacrylate, ethyleneglycol di(2-ethylacrylate), ethylene glycol di(2-propylacrylate),1,3-propylene glycol diacrylate, 1,4-butylene glycol diacrylate,1,5-pentanediol dimethacrylate, glycerol diacrylate, glyceroltriacrylate, trimethylolpropane triacrylate, trimethylolpropanetrimethacrylate, pentaerythritol diacrylate, pentaerythritoltriacrylate, pentaerythritol tetramethacrylate and pentaerythritoltetraaacrylate.

Closely related to the preceding acrylates are those which are derivedfrom di-, tri- and tetra-ethylene glycol and di- and tri-propyleneglycol. These compounds are those of formula II wherein X' is --O-- andA is alkylene oxy alkylene, and they may be more specificallyillustrated by the formula ##STR17## wherein R is hydrogen or a C₁ -C₃alkyl group, R' is hydrogen or methyl, n is 2 to 4 when R' is hydrogenand is 2 to 3 when R' is methyl. Representative of these compounds arediethylene glycol diacrylate, diethylene glycol dimethacrylate,triethylene glycol diacrylate, triethylene glycol dimethacrylate,tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate,dipropylene glycol diacrylate, dipropylene glycol dimethacrylate,triporpylene glycol diacrylate and tripropylene glycol dimethacrylate.

While a single unsaturated monomer may be employed alone in thephotopolymer composition, mixtures of two or more monomers are generallyemployed together to obtain best results. In any event the amount ofmonomer or monomers used to effect crosslinking of the polymer componentof the compositions of this invention will be from about 1 to about 50%,most preferably from about 5 to about 25%.

The photoinitiators useful in the photopolymer compositions of thisinvention are generally well known and some are characterized by beingphotoreducible. They are compounds which absorb actinic light verystrongly and thus becomes activated to the point where they willabstract hydrogen atoms from compounds which are hydrogen donors. By sodoing, the photoinitiator is itself reduced and the hydrogen donor isconverted into a free radical. Representative compounds arebenzophenone, 2-chlorobenzophenone, 4-methoxybenzophenone,4-methylbenzophenone, 4,4'-dimethylbenzophenone, 4-bromobenzophenone,2,2',4,4'-tetrachlorobenzophenone, 2-chloro-4'-methylbenzophenone,4-chloro-4'-methylbenzophenone, 3-methylbenzophenone,4-tert-butylbenzophenone, benzoin, benzoin methyl ether, benzoin ethylether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin acetate,benzil, benzilic acid, methylene blue, acetophenone,2,2-diethoxyacetophenone, 9,10-phenanthrenequinone, 2-methylanthraquinone, 2-ethyl anthraquinone, 2-tert-butyl-anthraquinone, and1,4-naphthoquinone. Particularly suitable are 2,2-diethoxyacetophenone,benzoin isopropyl ether, benzoin isobutyl ether, and 2-ethylanthraquinone. Also applicable are combinations of carboxyl sensitizercompounds and certain organic amine activators as disclosed in U.S. Pat.No. 3,759,807. In general, the photoinitiator should be thermally stableat temperatures up to about 100° C. Stability at such temperaturesprevents premature crosslinking when the compositions of this inventionare prepared or during storage. Such stability also minimizes, duringexposure, any crosslinking in the unexposed areas caused by the heatgenerated in the crosslinking reaction and by the heat transmittedthrough the opaque sections of the transparency. The amount ofphotoinitiator will be from about 0.1 to about 10%, most preferably fromabout 1.0 to about 10% by weight based on the weight of the polymer inthe photopolymer composition.

For the purpose of inhibiting premature crosslinking during thermalprocessing and storage of the photopolymer compositions of thisinvention, the incorporation of a thermal polymerization inhibitor andinhibitors is desirable. Such stabilizers also are well-known in theart, and they are exemplified by di-t-butyl-p-cresol, hydroquinonemonomethylether, pyrogallol, quinone, hydroquinone, methylene blue,t-butyl catechol, hydroquinone monobenzyl ether, methyl hydroquinone,amyl quinone, amyloxy hydroquinone, n-butyl phenol, phenol, hydroquinonemonopropyl ether, phenothiazine and nitrobenzene, used separately or incombination. When used in an amount within the range of from about 0.01to about 2% by weight of the polymer, these stabilizers are quiteeffective in preventing crosslinking of the photopolymer compositionduring processing and storage. During exposure such amounts ofstabilizer also delay and thus prevent crosslinking due to scatteredlight in the nonexposed areas of the composition, but do not greatlyinterfere with or delay the crosslinking of the composition in stronglyexposed areas, thus aiding in formation of a plate of optimum depth andsurface configuration.

The photopolymer compositions also may contain up to about 55% by weightof an inert particulate filler which is essentially transparent toactinic light. Representative of such fillers are the organophilicsilicas, the bentonites, silica and powdered glass, all having aparticle size less than 0.4 mil in their maximum dimension. Particles of0.1 micron or less in size are preferred. Such fillers can impartdesirable properties to the compositions and reliefs of this invention.Furthermore, the light scattering effected by the particulate fillersbroadens the image toward the base of the plate so that the half-tonedots take on the appearance of truncated cones in cross-section. Suchdots are stronger and have less tendency to break off than dots whichare more cylindrical in cross-section.

When the photopolymer compositions of this invention are exposed toactinic light at a wave length of from about 3000 to about 4000 Athrough a photographic negative or positive, the polymer beneath theexposed areas becomes insolubilized, whereas the polymer beneath theunexposed areas remains water dispersible. Subsequent washing of theplate removes the dispersible polymer, leaving a replica of the negativeor positive in relief. Washing will normally be carried out with diluteaqueous solution of an aionic or nonionic detergent. Anionic detergentssuch as α-olefin sulfonates, alkylaryl sulfonates, lauryl sulfate, alkylesters of sulfosuccinic acid, or sulfated ethylene oxide condensates ofalkyl phenols or fatty alcohols, and nonionic detergents such as alkylphenol, fatty alcohol or fatty acid ethylene oxide condensates may beused. α-olefin sulfonates are particularly useful. Detergentconcentrations of about 0.2 to 2% will normally be employed, generallyat temperatures of 25°-60° C. Development may frequently be acceleratedby brushing or scrubbing. In large scale work, application of the watersolvent will advantageously be carried out by means of jets or sprays.In some instances, it may be helpful to use minor quantities of organicsolvents such as the short chain aliphatic alcohols and ketones.Suitable solvents of these types include methanol, ethanol and acetone,and they generally will be used in amounts no greater than 25-35%,preferably less than 1-5% of the water or aqueous detergent developer.Following development of the plate, residual surface water, and anyorganic solvent which also might be present, may be removed by passing acurrent of warm air over the relief. In some instances it may bedesirable to post-expose or post-cure the plates by exposing to actiniclight at the wave lengths recited above, after the uncrosslinkedphotopolymer composition has been washed away.

The printing reliefs made in accordance with this invention are mostapplicable to those wherein a distinct difference in height betweenprinting and non-printing areas is required. These classes include thosewherein the ink is carried by the raised portion of the relief, such asin dry-set printing and ordinary letter-press printing. Because of theflexibility, abrasion resistance, resilience, and alcohol resistance ofthe relief plates prepared using these compositions, they areparticularly useful for flexographic printing in which alcohol basedinks are employed.

What I claim and desire to protect by Letters Patent is:
 1. The processof making a printing relief which comprises (1) admixing (a) a liquidterminal olefinically unsaturated linear polymer having a molecularweight in the range of from 1,000 to 20,000 selected from polymershaving the structure ##STR18## where X is selected from --O--, --S--,##STR19## and --NH-- groups; Y is selected from --O--CH₂ --CH═CH₂ and##STR20## R' is selected from --H and --CH₃ groups; Z is selected from##STR21## and ##STR22## where R" is selected from --H, --CH₃ and##STR23## and P is a polymer residue selected from homopolymers ofbutadiene, isoprene, chloroprene, styrene, isobutylene, ethylene, andcopolymers of butadiene with acrylonitrile, butadiene with styrene,butadiene with isoprene, ethylene with neohexene, isobutylene withstyrene, isobutylene with acrylonitrile, and the corresponding saturatedresidues; (b) from about 1 to about 50% by weight based on the weight ofthe polymer of at least one ethylenically unsaturated monomer selectedfrom acrylonitrile, methacrylonitrile, styrene, methyl substitutedstyrene and monomers containing one or more ##STR24## wherein R ishydrogen or a C₁ -C₃ alkyl group; (c) from about 0.1 to about 10% byweight based on the weight of the polymer of a photoinitiator, and (d)from about 0.01 to about 2% by weight based on the weight of the polymerof a stabilizer; (2) spreading the photopolymer composition in a layeron a support to form a photopolymer element, (3) exposing to actiniclight selected areas of said layer on said support until substantialcross-linking takes place in the exposed areas without significantcross-linking in the unexposed areas, and (4) removing the unexposedareas of photopolymer composition by washing the photopolymer elementwith an aqueous detergent solution.
 2. The process of claim 1 whereinresidual surface aqueous solution is removed by passing a current ofwarm air over the printing relief.
 3. The process of claim 1 wherein theprinting relief is post-exposed to actinitic light after the washing ofthe photopolymer element with an aqueous detergent solution.